Respirator canisters or cartridges are used to protect the health of military personnel, first responders and industrial workers from aerial chemical vapors. More than ten million respirator cartridges are being used each day in North America. It is desirable that a respirator canister includes an active indicator to indicate without ambiguity that the useful life of a canister has ended. However, currently commercially available canisters that protect against chemical vapors are not equipped with such an indicator. Without a device to monitor the sorption efficiency or protection provided by a canister to vapor penetration, a situation may arise where the sorption capacity of the canister is exceeded, rendering the canister ineffective and providing no protection without the user being aware that protection is no longer available.
Dye-based sensors to determine the remaining adsorption life of activated carbon in a canister exist, but these rely on a chemical reaction occurring with absorbed gases and are therefore limited to gases which undergo chemical reactions with the dyes.
The Eian U.S. Pat. No. 4,326,514 described a respirator canister or cartridge containing a gas/vapor sorbent bed with a colorimetric indicator strip positioned along a portion of an inner transparent sidewall of the cartridge. The colorimetric indicator is viewable through the transparent sidewall. The colorimetric indicator undergoes an irreversible change in color upon exposure to concentrations of select toxic vapors to which the sorbent bed is exposed. The indicator is effective at indicating the remaining capacity of the sorbent bed for toxic airborne material The indicator is, however, limited to toxic airborne material that undergoes a chemical reaction with the indicator strip.
The Bernard et al U.S. Pat. No. 6,375,725 described an end-of-service indicator for a respirator canister or cartridge having a gas/vapor sorbent bed (such a activated carbon) with an optical waveguide (optical fiber) located in the sorbent bed. One extremity of the waveguide is connected to a light source and the other to alight detector which measures the intensity of light transmitted by the waveguide. A portion of the outer layer of the waveguide is porous so that when the respirator cartridge is used in a toxic environment, the gas/vapor sorbent and the porous portion of the fiber gradually become saturated with absorbed gases. With absorption into the porous portion, the transmission of light through the fiber decreases. The detector senses the decrease in transmitted light and sends a signal to sound an alarm when the intensity of light measured by the detector is below a predetermined level. That alarm indicates that the sorbent is saturated and that the cartridge is at its effective end-of-service life. It should be noted that the end-of-service indicator acts on absorption and the resulting guidance losses of light in the fiber. As the absorption of gases into the porous outer layer of the fiber depends on the physical and chemical properties of the adsorbate, the extent of absorption, and consequently the sensitivity of the device is different for different toxic gases. Therefore, neither colormetric indicator strips nor optical fiber based indicators are completely non-selective as to the type of toxic environment to which a respirator cartridge is exposed, and consequently have limited applicability.